1. Field of the Invention
The present invention is related to mobile communication devices. In particular, the present invention relates to multi- or dual-mode wireless devices capable of both cellular and wireless local area network (WLAN) communications.
2. Discussion of the Related Art
Multimode or dual-mode handsets (i.e., handsets capable of both cellular and wireless LAN communications) have becoming popular recently. As homes, enterprises, and cities deploy wireless LAN networks, dual-mode handsets allow users to enjoy wide-area coverage mobility, faster networks, higher access rates and cheaper prices for both indoors and outdoor uses. Meanwhile, more Internet-based applications are ported to and run on dual-mode handsets; such applications include, for example, web browsing and Voice-over-IP (VoIP) applications. Therefore, users of multimode or dual-mode handsets may enjoy Internet access wherever they have broadband wireless access.
Although WLANs offer higher speed network access and cheaper services, wireless LAN communication requires higher power than cellular or cordless phones. Power consumption is a critical design consideration for handheld and other power resource-constrained devices. Prior art power management schemes in wireless LAN networks are known. For example, the IEEE 802.11 standard defines three basic modes for power management in wireless LAN networks: “wake-up” mode, “sleep” mode (also known as “dormant” mode), and power-save poll mode. In the IEEE 802.11 standard, there are two schemes for switching among these three modes: automatic power save delivery (APSD), and unscheduled automatic power save delivery (U-APSD) (See, for example, U.S. Pat. No. 6,917,598, entitled “Unscheduled Power Save Delivery Method In A Wireless Local Area Network For Real Time Communication,” issued on Jul. 12, 2005). Under the APSD scheme, the WLAN client switches from sleep mode to wake-up mode periodically to receive packets that have been buffered at an access point (AP) while the WLAN client is in sleep mode. In the U-APSD scheme, the WLAN client wakes up when it has packets to send out via an uplink, or when it expects to receive packets via a downlink. Once in the “awake” mode, the WLAN client notifies the AP to forward to it all packets that have been buffered while the WLAN client is in the sleep mode, and switches back to the sleep mode once the AP has sent all buffered packets.
Mode switching in the APSD and U-APSD schemes involves both the WLAN client and the WLAN AP, with the aim of minimizing the necessary wake-up time. Alternatively, a third scheme requires modification in the WLAN client only. Under that third scheme, a portion of the components within the WLAN client circuit is kept in an active mode to detect the RF signals from nearby APs, while the remainder of the WLAN client circuit is placed in the sleep mode until a strong WLAN RF signal is detected. (See, e.g., U.S. Pat. No. 6,754,194, entitled “Method and Apparatus for Indicating the Presence of a Wireless Local Area Network by Detecting Signature Sequences,” issued on Jun. 22, 2004.)
Because the mode-switching operation itself consumes significant power, when the number of packets that need to be delivered via wireless LAN is small, or when packet delivery is not synchronized with the mode-switching frequency, the power consumed due to frequent mode-switching under APSD is wasteful or the resulting response time may be delayed. Under a U-APSD scheme, when the number of packets to be sent is small, the application response time is delayed. For example, an incoming VoIP call would have to be buffered until a client has an outgoing packet to deliver.
Other research works disclose using application-specific power usage pattern to predict and adjust the processor speed to conform to the application's requirement and to adjust battery usage at the right level. See, for example, the article “Managing battery lifetime with energy-aware adaptation,” by Jason Flinn and M. Satyanarayanan, ACM Transactions on Computer Systems (TOCS), v. 22n. 2, p. 137-179, May 2004. Another example may be found in the article “Application-driven power management for mobile communication,” by Robin Kravets and P. Krishnan, published in Proceedings of the Fourth Annual ACM/IEEE International Conference on Mobile Computing and Networking (MobiCom) (Dallas, Tex., October 1998). Similarly, the Master's thesis (Mechanical Engineering), entitled “A reinforcement-learning approach to power management,” by C. Steinbach, in AI Technical Report, M. Eng Thesis, Artificial Intelligence Laboratory, MIT, May 2002, teaches using historic battery usage patterns of a device to predict its future power usage, and therefore to adjust the power mode to the appropriate level.
Using application-specific data or historical power requirement data to predict future power requirement may not be accurate in many instances. Further, a wrong prediction may result in inefficient, excessive power or erroneous processor speed for a given application. Also, because adjustments to correct power consumption itself are power-consuming as well, unnecessary or frequently power adjustments drain power quickly.
Still other research works disclose inter-working between different radio interfaces. (See, e.g., the article “MIRAI Architecture for Heterogeneous Network, IEEE Communications Maganize, by G. Wu, M. Mizuno, P. Havinga, February 2002.) The MIRAI architecture includes a common core network that connects multiple radio access networks (RANs). Each RAN may be homogeneous or heterogeneous. MIRAI uses a common signaling channel, known as the “Basic Access Network (BAN),” to co-ordinate among various radio networks. The BAN also provides location updates, paging, wireless network discovery, and support for heterogeneous handoff. U.S. Pat. No. 6,940,844, entitled “Method and apparatus for reporting WLAN capabilities of a dual mode GPRS/WLAN or UMTS/WLAN WTRU” presents a method for exchanging information regarding the network and terminal capabilities across the two network interfaces of dual-mode mobile terminals, so that service can be delivered to the terminal using the best interface and network. Other inter-working related prior art includes heterogamous handoffs. For example, U.S. Pat. No. 6,931,249, entitled “Method and apparatus for a target-initiated handoff from a source cellular wireless network to a target non-cellular wireless network” introduces a method to hand over from a cellular network to a non-cellular network.
MIRAI, however, remains a conceptual architecture. For control purpose, MIRAI requires a dedicated, common channel to be shared by all other radio interfaces. Current dual-mode handset systems lack such a dedicated, common channel to be used for control purpose. Further, in many cases, the cellular and the WLAN interfaces do not share the same core network as well.